How to test registration form in django?

Question

I have a test to check if registration form works correctly but user doesn't create. I don't understand why. For example if in test I use assertEqual(Profile.objects.last().user, 'test1'), it is said that it's Nonetype object. If I check response's status code, it is 200. So I can be sure that page works. And finally If I go to this register page and create a user with the same information by myself it will be created successfully.

What is the problem and how can I solve it?

Model:

class Profile(models.Model):
    user = models.OneToOneField(User, on_delete=models.CASCADE)
    city = models.CharField(max_length=36, blank=True)
    phone = models.IntegerField(blank=True)
    verification = models.BooleanField(default=False)
    quantity_posts = models.IntegerField(default=0)

    def __str__(self):
        return str(self.user)

    def get_absolute_url(self):
        return reverse('information', args=[str(self.pk)])

Form:

class RegisterForm(UserCreationForm):
    city = forms.CharField(max_length=36, required=False, help_text='Город')
    phone = forms.IntegerField(required=False, help_text='Сотовый номер')

    class Meta:
        model = User
        fields = ('username', 'city', 'phone', 'password1', 'password2')

View:

def register_view(request):
    if request.method == 'POST':
        form = RegisterForm(request.POST)
        if form.is_valid():
            user = form.save()
            city = form.cleaned_data.get('city')
            phone = form.cleaned_data.get('phone')
            Profile.objects.create(
                user=user,
                city=city,
                phone=phone,
            )
            username = form.cleaned_data.get('username')
            password = form.cleaned_data.get('password1')
            user = authenticate(username=username, password=password)
            login(request, user)
            return redirect('/')
    else:
        form = RegisterForm()
    return render(request, 'users/register.html', {'form': form})

part of main urls:

path('users/', include('app_users.urls'))

part of app urls:

path('register/', register_view, name='register')

test:

def test_if_can_register_profile(self):
    self.client.post('/users/register/', {
        'username': 'test1',
        'city': 'pavlodar',
        'phone': 87055551122,
        'password': 'Mypassword777',
        'password confirmation': 'Mypassword777'
    })
    self.assertTrue(Profile.objects.filter(user__username='test1').exists())